RMAN TARGET SYSBACKUP fails

Hi,

on 12C on Win2008 I have the following error when I try to connect to RMAN with SYSBACKUP :

C:\Windows\system32>RMAN TARGET SYSBACKUP

Recovery Manager: Release 12.1.0.1.0 - Production on Mer. Avr. 23 14:54:25 2014

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password:

RMAN-00571: ===========================================================

RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============

RMAN-00571: ===========================================================

RMAN-00554:

RMAN-04005:

ORA-01031: insufficient privileges

I ran :

grant sysbackup to sysbackup;

but did not change the situation.

but SYS can  :

C:\Windows\system32>RMAN TARGET SYS

Recovery Manager: Release 12.1.0.1.0 - Production on Mer. Avr. 23 14:55:03 2014

password :

connected to MYDB (DBID=2757634)

Thank for help.